Understanding inhomogeneous carbon impurity distribution on the surfaces of GaN nanorods

Carbon impurities are common surface defects in gallium nitride (GaN) optoelectronic devices and can strongly reduce luminescence efficiency. However, their distribution on different GaN surfaces and the underlying formation mechanisms remain unclear. Here, we use home-built photo-assisted Kelvin probe force microscopy to map carbon impurities on different surfaces of GaN nanorod. The results show that carbon incorporation is controlled by surface polarity and local strain. Nonpolar surfaces contain the highest carbon concentration, while semipolar surfaces show the lowest. Within polar surfaces, carbon is enriched at the center. Molecular dynamics and density functional theory calculations further indicate that tensile strain lowers CN formation energy, promoting carbon incorporation.